You need to use sudo to perform the operation since it requires root privileges. So instead of typing 'apt-get install pakagename' you need to use 'sudo apt-get install packagename'. It will prompt you for your password before elevating privileges and executing the apt-get command.

Update Manager click the "Settings" button. This will open your Software Sources windows:
1.Untick the "CD-ROM" option
2.Go through the list and untick all your PPAs
3.Then click close
4.see if you can now update successfully.